1. Field of the Invention
The present invention relates to an imager that photographs a subject with a rolling shutter.
2. Description of the Related Art
Japanese Unexamined Patent Publication (KOKAI) No. 2007-329604 discloses an image sensor that comprises photodiodes aligned on a square grid and photographs with a rolling shutter, and a contrast AF that relies on the contrast of image data output by the image sensor to determine whether a lens is focused on a subject. For examples, a CMOS image sensor is used as such an image sensor.
Meanwhile, the quality of a photographed image may be degraded by a flicker caused by a light source that changes its emitting intensity with the passage of time. For example, a fluorescent light is used as such a light source. To prevent degradation of image quality, a flicker included in a photographed image is detected.
The moment of exposure is different for each photodiode in the vertical direction because a CMOS image sensor photographs with a rolling shutter. Therefore, in the case that the intensity of a light source varies with respect to time, the amount of light received by each photodiode may be different in the vertical direction. In the case where the amount of received light differs, a contrast AF may cause interference because contrast in a photographed image is not consistent.